This invention relates to the art of tire pressure indicators and, more particularly to an improved warning device for indicating an unacceptable air pressure condition in either one of dual tires mounted on a common end of a vehicle axle.
Numerous devices have been devised heretofore for providing dual wheel assemblies on trucks, trailers, recreational vehicles and the like with a device or devices for indicating an undesirable tire pressure in one of the tires of the wheel assembly. In this respect, for example, U.S. Pat. Nos. 2,362,883 to Cecil and 2,463,335 to Warnshuis et al disclose dual tires connected in air flow communication with a common pressure sensor which, in response to an undesirably low air pressure condition in the tires, is operable to produce an audible or visual signal to indicate such condition. A major disadvantage of these mechanisms is that they operate to maintain an air pressure balance between the two tires whereby, when the undesirable low pressure is reached to actuate the alarm the vehicle operator has no way of determining whether one or the other or both of the tires is causing the pressure loss.
As another example, U.S. Pat. Nos. 3,527,189 to Perry and 4,646,673 to Fordice disclose low tire pressure indicating mechanisms comprising a discretely mounted pressure responsive device for each tire. Either a single indicator is released by one of the pressure responsive devices when the corresponding tire pressure is lower than desired, or a pair of indicators each associated with a corresponding one of the pressure responsive devices is released thereby when the corresponding tire pressure is unacceptably low. While these arrangements isolate the dual tires with respect to indicating a low pressure condition in either tire and, additionally, indicating to the vehicle operator which one of the two tires has the undesirably low pressure, they are structurally complex and expensive with respect to having to provide at least a pressure responsive device for each of the two tires and in most instances, a corresponding indicator for each of the pressure responsive devices.
As yet another example, U.S. Pat. Nos. 3,129,690 to Nygard and 3,958,526 to Liquie disclose low tire pressure indicating mechanisms including pressure responsive arrangements for releasing a single indicator in response to a low air pressure condition in one or the other tires of a dual wheel assembly. In Nygard, a tire air pressure balanced diaphragm responds to a low pressure condition in either one of the tires to release the indicator, and in Liquie each tire is provided with a corresponding pressure responsive device by which an inflatable indicator is displaced relative to the wheel assembly in response to a low pressure condition in either tire. Neither of these devices is operable to indicate which of the two tires has the low pressure condition, and the Nygard device is inoperable in a situation where both tires have the same air pressure even if such pressure is below a desired pressure.